Neutrino crown of a protoneutron star in the process of collapse: Physical formulation of the problem

Abstract

A spherically symmetric gravitational collapse of the iron core of a star develops in the form of a hydrodynamic process, where the role of intrinsic neutrino radiation ever increases. The early stage of the collapse has a homological character within the interior of the core, but there is a delay in exterior layers. Hydrodynamic calculations reveal that, at the late stage of the collapse (it is the stage within which the majority of neutrinos are emitted), a structure is formed that consists of a neutron-star germ nontransparent to neutrinos and exterior layers accreting onto it, which are, on the contrary, transparent to neutrinos. They are separated by a semitransparent layer occurring between the front of the accretion shock wave and the germ surface forming a neutrinosphere. By using a typical quasistationary character of this layer, which is referred to as the neutrino crown of a protoneutron star, a stationary model is developed here that supplements hydrodynamic calculations of the collapse process, which are rather rough within this model. In particular, these calculations reveal the crucial significance of the semitransparent crown for a possible transition of the collapse into an explosion having a scale of a supernova explosion. If there is no such possibility, the same crown determines the important properties of a quiet collapse that are associated with the development of convective instability, etc., in it. The model formulated here, which is comparatively simple (in relation to hydrodynamic calculations) owing to an adequate physical formulation of problem, is intended for analyzing special features of the crown. This formulation of the problem demonstrates some new possibilities of neutrino hydrodynamics, which is an analog of the well-known radiative hydrodynamics involving photons instead of neutrinos.